Myodural Bridge Research Articles

Evaluation of the Structure of Myodural Bridges in an Equine Model of Ehlers-Danlos Syndromes

Myodural bridges have been described in various species as connective tissue structures “bridging” small cranio-cervical muscles to the dura. Myodural bridges are thought to stabilize the dural sac during head and neck movements and promote cerebrospinal fluid motion; however, their role in neurological diseases has not yet been established. We report ultrasonographic visualization, necropsy, histopathologic and ultrastructural findings of myodural bridges in horses with hereditary equine regional dermal asthenia (HERDA), an equine model of Ehlers-Danlos syndromes. Five HERDA and 5 control horses were studied. Post-mortem examination and ultrasonographic studies (3 HERDA and 4 controls) demonstrated that the atlanto-occipital and atlanto-axial myodural bridges are dynamic structures “moving” the dura. En block resection of the myodural bridges (4 HERDA and 5 controls) was accomplished and histopathology showed myofiber degeneration in 3 HERDA horses and 1 control. Ultrastructural examination revealed loosely packed collagen fibrils with abnormal orientation in all HERDA horses compared to mild abnormalities in 2 controls. Our study provides necropsy and ultrasonographic evidence of the dynamic aspect of the myodural bridges as dural sac stabilizers. Myodural bridges may be pathologically altered in connective tissue disease as evidenced by the ultrastructural morphology in the HERDA myodural bridge.

Suboccipital myodural bridges revisited: Application to cervicogenic headaches.

There seems to be no complete demonstration of the suboccipital fascial configuration. In 30 human fetuses near term, we found two types of candidate myodural bridge: (1) a thick connective tissue band running between the rectus capitis posterior major and minor muscles (rectus capitis posterior major [Rma], rectus capitis posterior minori [Rmi]; Type 1 bridge; 27 fetuses); and (2) a thin fascia extending from the upper margin of the Rmi (Type 2 bridge; 20 fetuses). Neither of these bridge candidates contained elastic fibers. The Type 1 bridge originated from: (1) fatty tissue located beneath the semispinalis capitis (four fetuses); (2) a fascia covering the multifidus (nine); (3) a fascia bordering between the Rma and Rmi or lining the Rma (13); (4) a fascia covering the inferior aspect of the Rmi (three); and (5) a common fascia covering the Rma and obliquus capitis inferior muscle (nine). Multiple origins usually coexisted in the 27 fetuses. In the minor Type 2 bridge, composite fibers were aligned in the same direction as striated muscle fibers. Thus, force transmission via the thin fascia seemed to be effective along a straight line. However, in the major Type 1 bridges, striated muscle fibers almost always did not insert into or originate from the covering fascia. Moreover, at and near the dural attachment, most composite fibers of Type 1 bridges were interrupted by subdural veins and dispersed around the veins. In newborns, force transmission via myodural bridges was likely to be limited or ineffective. The postnatal growth might determine a likely connection between the bridge and headache. Clin. Anat. 32:914-928, 2019. © 2019 Wiley Periodicals, Inc.

Existence and features of the myodural bridge in Gallus domesticus: indication of its important physiological function.

The myodural bridge (MDB) is a dense connective tissue that connects muscles with the cervical spinal dura mater via the posterior atlanto-occipital and atlato-axial interspaces. To date, the physiological function of the MDB has not been fully elucidated. Recent studies have identified the presence of the MDB in mammals, but very little information is available on the existence of the MDB in avifauna. We selected Gallus domesticus to explore the existence and the fiber property of the MDB in avifauna. We found that in this species, fibers originating from the ventral aspect of the rectus capitis dorsal minor are fused with the dorsal atlanto-occipital membrane and that numerous trabeculae connect the dorsal atlanto-occipital membrane with the cervical spinal dura mater. Furthermore, the occipital venous sinus is located between the trabeculae. The MDB is mainly composed of collagen type I fibers. Our results show that the MDB is present in G. domesticus and lead us to infer that the MDB is a highly conservative evolutionary structure which may play essential physiological roles.

The myodural bridge in the common rock pigeon (Columbia livia): Morphology and possible physiological implications.

The dense connective tissue that connects muscles to the cervical spinal dura mater is known as the myodural bridge in human anatomy and has been a subject of interest to anatomists and clinicians. The myodural bridge was originally discovered in humans, and also has been observed in other mammals and in reptilian sauropsids. We investigated the existence of the myodural bridge in a bird, that is, the Common Rock Pigeon Columba livia, to expand the understanding of the structure and function of the myodural bridge. Gross anatomical dissection of seven specimens and histological analyses of the suboccipital region of eight specimens were performed. The rectus capitis dorsalis minor muscle joins occipital periosteal extensions and inserts with several dense connective tissue cords on the dorsal side of the dura mater of the cervical spinal cord. The myodural bridge consists primarily of collagen Type I fibres, suggesting that the myodural bridge can transmit strong tensional forces generated by the contraction of M. rectus capitis dorsalis minor to the dura mater. The pull on the dura mater may affect the circulation of the cerebrospinal fluid in the subarachnoid space of the spine.

Anatomical Parameters of the Rectus Capitis Posterior Major and Obliqus Capitis Inferior Muscles Based on an Oblique Sagittal Magnetic Resonance Scan Method

The deep suboccipital muscles has been shown to connect the spinal dura mater via dense connective tissue termed the myodural bridge (MDB). The MDB has both physiological and clinical implications. Data on morphological and imaging anatomical parameters of the deep suboccipital muscles are scare. In this study, T2-weighted images of rectus capitis posterior major (RCPma) and obliqus capitis inferior (OCI) of 109 healthy adults were obtained by 0-degree sagittal and 30-degree oblique sagittal continuous MRI scanning of the head and neck of the subjects. Sectional area parameters of the RCPma and the OCI were measured. The 0-degree sagittal section was measured with 5 mm bias from the median sagittal plane, the sectional area of the RCPma was 186.34± 55.02 mm2 on the left, and 202.35± 59.76 mm2 on the right. The sectional area of OCI was 221.72± 68.99 mm2 on the left, and 224.92± 61.34 mm2 on the right; At the section with 30-degree bias from the oblique sagittal plane, the sectional area of RCPma was 183.30± 42.24 mm2 in males, and 133.05± 26.44 mm2 in females. The sectional area of OCI was 254.81± 46.20 mm2 in males, and 167.42± 27.85 mm2 in females. Significant sex difference exists in the sectional areas of the RCPma and OCI, the values of the male subjects were predominantly larger (P < 0.05), however there were no age- related significant difference. The sectional area of RCPma is bilateral asymmetric, the RCPma on the right side is larger than that of the left side (P < 0.05), but the OCI is bilaterally symmetric (P >0.05). The MRI image features, imaging anatomical data and sexual dimorphism of the RCPma and the OCI are presented in this study. This imaging anatomical data will be useful for functional and clinical studies on the RCPma, OCI, and the MDB.

The myodural bridges' existence in the sperm whale.

Recent studies have identified that the myodural bridge (MDB) is located between the suboccipital muscles and cervical dura mater in the posterior atlanto-occipital interspace within humans. The myodural bridge has been considered to have a significant role in physiological functions. However, there is little information about the myodural bridge in marine mammals; we conducted this study to investigate and examine the morphology of the myodural bridge in a sperm whale. We also aim to discuss the physiological functions of the myodural bridge. In this study, a 15.1-meter long sperm whale carcass was examined. Multiple methods were conducted to examine the bridges of the sperm whale which included dissection, P45 plastination and histological analysis. This study confirmed the existence of the myodural bridge in the sperm whale and shows there are two types of the bridge in the sperm whale: one type was the occipital-dural bridge (ODB), the other type was the MDB. A large venous plexus was found within the epidural space and this venous plexus is thought to contain a great amount of blood when in deep water and thus the movements of suboccipital muscles could be a unique power source that drives cerebrospinal fluid circulation.

Orientation and property of fibers of the myodural bridge in humans

Background ContextStudies over the past 20 years have revealed that there are fibrous connective tissues between the suboccipital muscles, nuchal ligament, and cervical spinal dura mater (SDM). This fibrous connection with the SDM is through the posterior atlanto-occipital or atlantoaxial interspaces and is called the myodural bridge (MDB). Researchers have inferred that the MDB might have important functions. It was speculated that the function of MDB might be related to proprioception transmission, keeping the subarachnoid space and the cerebellomedullary cistern unobstructed, and affecting the dynamic circulation of the cerebrospinal fluid. In addition, clinicians have found that the pathologic change of the MDB might cause cervicogenic or chronic tension-type headache. Previous gross anatomical and histologic studies only confirmed the existence of the MDB but did not reveal the fiber properties of the MDB. This is important to further mechanical and functional research on the MDB. PurposeMultiple histologic staining methods were used in the present study to reveal the various origin and fiber properties of the MDB. Muscles and ligaments participating in forming the MDB at the posterior atlanto-occipital or atlantoaxial interspaces were observed, and the fiber properties of the MDB were confirmed. The present study provides a basis for speculating the tensile force values of the MDB on the SDM and a morphologic foundational work for exploring the physiological functions and clinical significances of the MDB. Study DesignAnatomical and histologic analyses of suboccipital structures that communicate with the SDM at the posterior atlanto-occipital or atlantoaxial interspaces were carried out. MethodsMultiple histologic staining methods were used to evaluate the histologic properties and composition of the MDB at the posterior atlanto-occipital or atlantoaxial interspaces in five formalin-fixed head-neck human specimens. ResultsThe results show that the MDB traversing the atlanto-occipital interspace originated from the rectus capitis posterior minor (RCPmi). The MDB traversing the atlantoaxial interspace originated mainly from the RCPmi, rectus capitis posterior major, and obliquus capitis inferior. These fibers form the vertebral dural ligament in the atlantoaxial interspace and connect with SDM. The MDB is mainly formed by parallel running type I collagen fibers; thus, suboccipital muscle could pull SDM strongly through the effective force propagated by the MDB during head movement. ConclusionsMyodural bridge is mainly formed by parallel running type I collagen fibers; thus, it can transmit the strong pull from the diverse suboccipital muscles or ligaments during head movement. The results of the present study will serve as a basis for further biomechanical and functional MDB research.

The universal existence of myodural bridge in mammals: an indication of a necessary function

The “myodural bridge” was described in literatures as a dense fibrous tissue connecting the sub-occipital musculature with the spinal dura mater in human studies. Now the concept of “myodural bridge” was perceived as an exact anatomical structure presumably essential for critical physiological functions in human body, and might exist in other mammals as well. To determine the existence of the “myodural bridge” in other mammals and to lay a foundation for the functional study, we examined representatives in five different mammalian orders. Based on the anatomical dissections, P45 plastinated sections and histological sections, we found that a dense fibrous tissue connected the rectus capitisdorsalis minor and the spinal dura mater through the dorsal atlanto-occipital interspace with or without the medium of the posterior atlanto-occipital membrane. These observed connective tissues were very similar to the “myodural bridge” previously described in humans. We proposed that the “myodural bridge”, as an evolutionally conserved structure, presents in many other mammals. Moreover, we believed that the “myodural bridge” might be a homologous organ in mammals. Thus, this study could provide an insight for our understanding the physiological significance of the “myodural bridge”, especially in human.

The second terminations of the suboccipital muscles: An assistant pivot for the To Be Named Ligament.

In the last two decades, many studies have focused on the muscles and dense connective tissues located in the suboccipital region. Our study investigated the existence of the second terminations originating from the suboccipital muscles, and the relationship between the variable types of the To Be Named Ligament (TBNL). Anatomical dissection was performed on 35 head-neck specimens. The existence of the second terminations of the suboccipital muscles was confirmed and various types of the TBNL were observed in this study. The second terminations originated from multiple suboccipital muscles including the rectus capitis posterior minor (RCPmi), rectus capitis posterior major (RCPma) and obliquus capitis inferior (OCI) muscles, merged and terminated at the TBNL. The overall incidence of the second terminations of the suboccipital muscles was 34.29% and it varied among the various suboccipital muscle origins. 28.57% of the second terminations originated from the RCPma; 11.43% was from the RCPmi and 8.57% was from the OCI. Furthermore, there was a significant relationship between the existence of second terminations and the particular type of the TBNL. 95% of the arcuate type of the TBNL was accompanied with the second terminations which attached to their turning part, whereas only 10% of all the radiate type of the TBNL was accompanied with the second terminations. This study for the first time described the second terminations originating from multiple suboccipital muscles and demonstrated the relationship with the various types of the TBNL. We speculated that the second terminations maintain the arcuate TBNL and transfer tensile forces to the Myodural Bridge (MDB), thereby modulating the physiological functions of the MDB.

The myodural bridge existing in the Nephocaena phocaenoides.

Recent studies have identified that the myodural bridge (MDB) between the rectus capitis posterior minor (RCPmi) and the cervical spinal dura mater in the posterior atlanto-occipital interspace in humans. And it was supposed that the MDB may play essential physiological roles. As a result, the MDB is possibly a highly conserved structure in the evolution of mammals. However, there is little confirmative description about the existence of the MDB in marine mammals. The objective of this study was to explore the existence and the fiber property of the MDB in the Neophocaena phocaenoides. Six cadavers of the Neophocaena phocaenoides with formalin fixation were used in this study. One was used for head and neck CT scanning and three-dimensional (3D) reconstruction and suboccipital region dissection, two were for sectional observation by P45 plastinated sheets of head and neck, and three were for histological analysis of suboccipial structures. This is the first study to demonstrate the existence of the MDB in the aquatic mammals. The rectus capitis dorsal minor (RCDmi) originated from the inferior border of the occiput and inserted into the cervical spinal dura mater. At the ventral aspect of the RCDmi, the MDB directly extended through the posterior atlanto-occipital interspace and connected with the cervical spinal dura mater which was consisted of type Ⅰ collagen. In addition, the dorsal atlanto-occipital membrane was not found in the Neophocaena phocaenoides. The tendinous myodural bridge extended from the RCDmi to the spinal dura mater through the posterior atlanto-occipital interspace in the Neophocaena phocaenoides.

A Systematic Review of the Soft-Tissue Connections Between Neck Muscles and Dura Mater: The Myodural Bridge.

Systematic review. To elucidate the existence of soft tissue connections between the neck muscles and cervical dura mater. Several studies discuss the existence of a cervical myodural bridge; however, conflicting data have been reported. Searches were conducted in the PubMed, Web of Science, Cochrane Library, and PEDro databases. Studies reporting original data regarding the continuity of non-post-surgical soft tissue between the cervical muscles and dura mater were reviewed. Two reviewers independently selected articles, and a third one resolved disagreements. Another two researchers extracted the methodology of the study, the anatomical findings, and evaluated the quality of the studies using Quality Appraisal for Cadaveric Studies Scale. A different third researcher resolved disagreements. Twenty-six studies were included. A soft tissue connection between the rectus capitis posterior minor, the rectus capitis posterior major, and the obliquus capitis inferior muscles seems to be proved with a strong level of evidence for each one of them. Controversy exists about the possible communication between the dura mater and the upper trapezius, rhomboideus minor, serratus posterior superior, and splenius capitis by means of the ligamentum nuchae. Finally, there is limited evidence about the existence of a soft tissue connection between rectus capitis anterior muscle and the dura mater. There is a continuity of soft tissue between the cervical musculature and the cervical dura mater; this might have physiological, pathophysiological, and therapeutic implications, and going some way to explaining the effect of some therapies in craniocervical disorders. N/A.

Head movement, an important contributor to human cerebrospinal fluid circulation

The suboccipital muscles are connected to the upper cervical spinal dura mater via the myodural bridges (MDBs). Recently, it was suggested that they might work as a pump to provide power for cerebrospinal fluid (CSF) circulation. The purpose of this study was to investigate effects of the suboccipital muscles contractions on the CSF flow. Forty healthy adult volunteers were subjected to cine phase-contrast MR imaging. Each volunteer was scanned twice, once before and once after one-minute-head-rotation period. CSF flow waveform parameters at craniocervical junction were analyzed. The results showed that, after the head rotations, the maximum and average CSF flow rates during ventricular diastole were significantly increased, and the CSF stroke volumes during diastole and during entire cardiac cycle were significantly increased. This suggested that the CSF flow was significantly promoted by head movements. Among the muscles related with head movements, only three suboccipital muscles are connected to the upper cervical spinal dura mater via MDBs. It was believed that MDBs might transform powers of the muscles to CSF. The present results suggested that the head movements served as an important contributor to CSF dynamics and the MDBs might be involved in this mechanism.

Connection of the Posterior Occipital Muscle and Dura Mater of the Siamese Crocodile.

The myodural bridge was proposed initially in 1995. The myodural bridge is a connective tissue bridge that connects a pair of deep muscles at the suboccipital region to the dura mater. There have been numerous studies concerning the morphology and function of the myodural bridge. To determine whether a myodural bridge exists in reptiles, six Siamese crocodiles were investigated using gross anatomy dissection and P45 sheet plastination technologies. As a result, we demonstrated that the posterior occipital muscles of the Siamese crocodile are directly or indirectly connected to the proatlas, atlas, and intermembrane between them. Multiple trabeculae existing in the posterior epidural space extended from the ventral surface of the proatlas, atlas, and intermembrane between them to the dorsal surface of the spinal dura mater. This study showed that the posterior occipital muscle in the suboccipital region of the Siamese crocodile is connected to the spinal dura mater through the proatlas, atlas, and the trabeculae. In conclusion, a myodural bridge-like structure exists in reptiles. This connection may act as a pump to provide cerebrospinal fluid (CSF) circulation at the occipitocervical junction. We hypothesize that a physiologic role of the Siamese crocodile's myodural bridge may be analogous to the human myodural bridge. Anat Rec, 299:1402-1408, 2016. © 2016 Wiley Periodicals, Inc.

Effect of the Suboccipital Musculature on Symptom Severity and Recovery after Mild Traumatic Brain Injury.

Neck musculature mass has been suggested as a biomechanical contributor to injury severity in mild traumatic brain injury. We sought to determine how the cross-sectional areas of the suboccipital muscles affect symptom severity, neurocognitive performance, and recovery time in patients with mild traumatic brain injury. Sixty-four consecutive patients with mild traumatic brain injury underwent MR imaging and serial neurocognitive testing with the Immediate Post-Concussion Assessment and Cognitive Test. Cross-sectional areas of the rectus capitis posterior musculature were retrospectively obtained at C1, and cross-sectional areas of the remaining 7 suboccipital muscles were measured at C2. Cross-sectional area reproducibility was evaluated. Overall and individual muscle cross-sectional areas were correlated with symptom severity, neuropsychological testing, recovery time, and headache. Sixty-four patients with mild traumatic brain injury had imaging through C1, and 43 had imaging through C2. Reproducibility of cross-sectional area measurements was substantial (correlation coefficients = 0.9517-0.9891). Lower cross-sectional area of the rectus capitis posterior minor was correlated with greater symptom severity (r = 0.596, P < .0001), longer recovery time (r = 0.387, P = .002), poor verbal memory performance (r = 0.285, P = .02), and headache (r = 0.39, P = .001). None of the other cross-sectional areas were associated with symptom severity, recovery time, neurocognitive testing, or headache. In mild traumatic brain injury, the rectus capitis posterior minor is the only suboccipital muscle whose cross-sectional area is associated with symptom severity and worse outcome. Given the unique connection of this muscle to the dura, this finding may suggest that pathology of the myodural bridge contributes to symptomatology and prognosis in mild traumatic brain injury.

Patterns of attachment of the myodural bridge by the rectus capitis posterior minor muscle.

The myodural bridge was first described by Hack in 1995 and was thought to be related to chronic cervicogenic headaches. For a long time, few studies revealed the patterns of the myodural bridge considering the rectus capitis posterior minor muscle. In this study, P45 plastination technology and anatomical dissection were performed on head specimens, and four different terminal region types of the rectus capitis posterior minor muscle were observed, including the posterior atlanto-occipital interspace, posterior arch of the atlas and posterior atlanto-axial interspace. We propose that the myodural complex structures in the posterior atlanto-occipital and posterior atlanto-axial interspace have cooperative effects on cerebrospinal fluid and work together. This force might be an important source for the circulation of cerebrospinal fluid.

Histological examination of the human obliquus capitis inferior myodural bridge

This study was designed to examine the anatomical relationship between the obliquus capitis inferior (OCI) muscle and the cervical dura mater at the histological level. Eight human cadavers, with an average age of 65 ± 7.9 years were selected from a convenience sample for suboccipital dissection. Twelve OCI muscle specimens were excised, 100% of which emitted grossly visible soft tissue tracts that inserted into the posterolateral aspect of the cervical dura. These 12 myodural specimens were excised as single, continuous structures and sent for H&E staining. One sample also underwent immuno-peroxidase staining. Microscopic evaluation confirmed a connective tissue bridge emanating from the OCI muscular body and attaching to the posterolateral aspect of the cervical dura mater in 75% of the specimens. Microtome slices of the remaining 25% were not able to capture muscle, connective tissue and dura within the same plane and were therefore unable to be properly analyzed. The sample sent for neuro-analysis stained positively for several neuronal fascicles traveling within, and passing through the OCI myodural bridge. This study histologically confirms the presence of a connective tissue bridge that links the OCI muscle to the dura mater and the presence of neuronal tissue within this connection warrants further examination. This structure may represent a component of normal human anatomy. In addition to its hypothetical role in human homeostasis, it may contribute to certain neuropathological conditions, as well.

The obliquus capitis inferior myodural bridge

This study was designed to examine the obliquus capitis inferior (OCI) muscle from a gross anatomical perspective. The objective was to isolate and identify the OCI myodural bridge, while examining its course and contributing elements. An earlier study of the posterior cervical spine briefly reported a connection between the OCI and the cervical dura mater. To the best of our knowledge, a study has not yet been conducted specifically on this muscle and its relation to the dura mater. In this study, the suboccipital regions of nine embalmed cadavers were dissected. A total of 14 OCI muscles were isolated for examination. All findings were documented via photograph. Of the 14 OCI muscles isolated, all emitted fibrous tissue bands from the anterolateral portion of the muscular belly. These fibers attached to the posterolateral cervical dura mater by route of the atlantoaxial interspace. The OCI myodural bridge appeared to coalesce with the rectus capitis posterior major myodural bridge, giving the appearance of a single atlantoaxial structure that links these two muscles to the dura mater. In conclusion, the OCI was attached to the dura mater in all of the 14 muscle specimens. We hypothesize that the OCI myodural bridge may play a physiological role in monitoring dural tension and preventing dural infolding. It may also contribute to certain clinical symptoms manifesting from alterations in dural tone.

Connection between the spinal dura mater and suboccipital musculature: Evidence for the myodural bridge and a route for its dissection—A review

A connective tissue link between the spinal dura mater and the rectus capitis posterior minor muscle was first described in 1995 and has since been readily demonstrated via dissection, magnetic resonance imaging, and plastinated cross-sections of the upper cervical region (Hack et al. [1995] Spine 20:2484-2486). This structure, the so-called "myodural bridge," has yet to be included in any of the American anatomy textbooks or dissection guides commonly used in medical education. This direct anatomic link between the musculoskeletal system and the dura mater has important ramifications for the treatment of chronic cervicogenic headache. This article summarizes the anatomic and clinical research literature related to this structure and provides a simple approach to dissect the myodural bridge and its attachment to the posterior atlanto-occipital membrane/spinal dura mater complex and summarizes the case for its possible inclusion in medical anatomy curricula.

Post-traumatic upper cervical subluxation visualized by MRI: a case report.

BackgroundThis paper describes MRI findings of upper cervical subluxation due to alar ligament disruption following a vehicular collision. Incidental findings included the presence of a myodural bridge and a spinal cord syrinx. Chiropractic management of the patient is discussed.Case presentationA 21-year old female presented with complaints of acute, debilitating upper neck pain with unremitting sub-occipital headache and dizziness following a vehicular collision. Initial emergency department and neurologic investigations included x-ray and CT evaluation of the head and neck. Due to persistent pain, the patient sought chiropractic care. MRI of the upper cervical spine revealed previously unrecognized clinical entities.ConclusionThis case highlights the identification of upper cervical ligamentous injury that produced vertebral subluxation following a traumatic incident. MRI evaluation provided visualization of previously undetected injury. The patient experienced improvement through chiropractic care.